Mr. Matthew Totaro Legacy High School Chemistry Nuclear Chemistry Mr. Matthew Totaro Legacy High School Chemistry

The Discovery of Radioactivity Antoine-Henri Becquerel designed an experiment to determine if phosphorescent minerals also gave off x-rays.

The Discovery of Radioactivity, Continued Bequerel discovered that certain minerals were constantly producing penetrating energy rays he called uranic rays. Like x-rays. But not related to fluorescence. Bequerel determined that: All the minerals that produced these rays contained uranium. The rays were produced even though the mineral was not exposed to outside energy. Energy apparently being produced from nothing?

The Discovery of Radioactivity, Continued Marie Curie used an electroscope to detect the radiation of uranic rays in samples. By carefully separating minerals into their components, she discovered new elements by detecting the radiation they emitted. Radium named for its green phosphorescence. Polonium named for her homeland. Since the radiation was no longer just emitted from of uranium, she renamed it radioactivity.

What Is Radioactivity? Radioactivity = release of tiny, high-energy particles from an atom. Particles are ejected from the nucleus.

Properties of Radioactivity Radioactive rays can ionize matter. Cause uncharged matter to become charged. Radioactive rays have high energy. Radioactive rays cause phosphorescent chemicals to glow. Types of Radioactive Rays: Alpha (ά) Beta (β) Gamma (γ) Positron (b+)

Alpha Emission (Decay) An ά particle contains 2 protons and 2 neutrons. Helium nucleus. Stopped by skin or sheet of paper Loss of an alpha particle means: Atomic number decreases by 2. Mass number decreases by 4.

ά Decay

Beta Emission (Decay) A β particle is like an electron, BUT Moving much faster Produced from the nucleus Stopped by few sheets of aluminum foil or glass When an atom loses a β particle, its: Atomic number increases by 1 Mass number remains the same In beta decay, a neutron changes into a proton

β Decay

Gamma Emission Gamma (ϒ) rays are high-energy photons of light Stopped by several centimeters of lead No loss of particles from the nucleus No change in the atomic number and mass number Does not occur alone Will accompany an α or β decay

Positron Emission (Decay) Positron has a charge of 1+ c.u. and negligible mass. Anti-electron. When an atom loses a positron from the nucleus, its: Mass number remains the same. Atomic number decreases by 1. Positrons appear to result from a proton changing into a neutron.

Positron b+ Decay

g a, b, He e Types of Radiation Symbol 4 0.00055 Charge +2 -1 Type of Radiation Alpha particle Beta particle Gamma ray Symbol a, b, g Mass (amu) 4 0.00055 Charge +2 -1 4 He e 2 -1

Penetrating Ability Alpha particle stopped by skin or sheet of paper Beta particle stopped by few sheets of aluminum foil Gamma ray stopped by several centimeters of lead

Important Atomic Symbols Particle Symbol Nuclear symbol Proton p+ Neutron n0 Electron e- Alpha a Beta b, b- Positron b, b+